This invention is directed to the field of limited slip differentials of the type for connecting a vehicle""s driving shaft to a pair of driven shafts, but more particularly to a limited slip differential that incorporates a self contained lubricant supply isolated from the lubricant disposed in the differential housing or carrier.
The present invention relates to an improved limited slip differential of the type for use in vehicular applications, such as automobiles. By way of brief background, when an automobile goes around a comer, the outer driving wheel must be turned at a greater speed than the inner one. This is achieved through the differential. It lies midway between the two driving wheels, linked to each wheel by a half-shaft turned through a bevel gear. The half-shafts have sun gears connected by free-wheeling planet pinions. When traveling straight, the planet pinions do not spin and drive both half-shafts at the same speed. As the automobile corners, the planet pinions do spin, driving the sun gear and half-shafts at different speeds.
Such differential systems have been improved over the years. Of particular concern to automotive engineers is the problem of traction, such as when one driving wheel encounters ice, mud, or snow, and the like. In straight, dry driving conditions, the differential supplies equal torque to each half-shaft. However, when adverse driving conditions are encountered, such as operating on a slippery surface, prior art differentials, supplying equal torque to the driving wheels resulted in reduced traction even when only one driving wheel was exposed to the slippery road surface. This dangerous condition resulted in the development of differential systems that introduced a torque to the system. The respective developments have become what are known as limited slip differentials, where the following prior art represents the state of the art on limited slip differentials. Such prior art, listed as U.S. Patents, are as follows:
a.) U.S. Pat. No. 6,076,646, to Bums, discloses a hydraulic coupling for use in motor vehicle driveline applications to limit speed differentiation and transfer drive torque between two rotary members. The hydraulic coupling includes a multi-plate clutch assembly operably connecting the two relatively rotatable members, and a sealed actuator assembly for actuating the clutch assembly in response to the magnitude of speed differentiation between the two rotary members. The actuator assembly includes a hydraulic pump and a piston, which are sealed relative to the clutch assembly. The sealed actuator assembly includes an internal recirculation path for supplying hydraulic fluid retained therein between a low pressure supply chamber at the inlet side of the hydraulic pump and a high pressure piston chamber provided at the discharge side of the hydraulic pump. Hydraulic pressure in the piston chamber controls the magnitude of the clutch engagement force exerted by the piston on the clutch assembly. As a further feature, the recirculation path includes a flow restrictor which provides a bleed flow path for supplying high pressure fluid from the piston chamber to the supply chamber following cessation of the pumping action to release the clutch assembly.
b.) U.S. Pat. No. 4,245,525, to LeBegue, teaches a pair of differential side gears splined to separate driven shafts that rotate the driven wheels of a vehicle. Rotation of a driven shaft is transmitted through a differential case and spider gears to the side gears. The side gears are rotatably mounted on a thrust assembly. Belleville spring assemblies exert a biasing force upon interleaved clutch plates alternately spined to the case and the side gears. Upon the occurrence of an unequal torque distribution between the driven shafts the gear separating forces exerted by the spider gears upon the side gears become imbalanced. The side gear associated with the driven shaft of the wheel having reduced traction is displaced axially toward the spider gears. This axial movement is transmitted through the thrust assembly to the side gear associated with the driven shaft of the wheel having the greater traction to axially move the side gear and compress the clutch plates to frictionally engage the case and the side gear. Rotation is transmitted from the case through the clutch plates to the side gear to increase the torque of the driven shaft of the wheel having the greater traction and thereby rotate the wheel having the greater traction.
c.) U.S. Pat. No. 3,896,684, to Duer, relates to a non-chattering limited slip differential which includes a clutch pack with alternating clutch plates of two types, one type being a conventional annular clutch plate. The other type comprises inner and outer annular members joined in a neck section which allows relative movement between the members. The outer member has an indentation diametrically opposite the neck section and the inner member has a tab projecting radially outward into the indentation to limit the relative movement between the members.
While the prior art offer different approaches to improving the operation and performance of differentials for vehicular applications, none are directed to the unique system for a limited slip differential casing that contains separate chambers, isolated in fluid sealing relationship from one another, and specifically to a sealing arrangement that isolates the lubricant in the differential case from the lubricant in the differential carrier. The manner by which the present invention achieves these goals will become clearer in the specification which follows.
This invention relates to an improved limited slip differential, as employed in the driving mechanism of vehicles, and to a method for providing a limited slip differential that has reduced chattering noise without deteriorating seal integrity.
The invention comprises a lubricant containing rotating case receiving a pair of output shafts for rotating the vehicle wheels, and a side gear, pinion gear and friction plates for each of the output shafts. Power to the output shafts is achieved by the rotating case revolving the pinion gears which in turn rotate the side gears. The rotating case is rotatably disposed within a differential carrier.
The improved feature hereof is the provision of an isolated first chamber defined by the interior of the rotating case, isolated from the chamber defined between the differential case and the carrier, where each chamber bathes selected components within a separate lubricating medium. Specifically, the side gear, pinion gear and friction plates are positioned within a first of the chambers. Fluid seals are provided between each axle and the axle openings in the differential case (trunnions) to isolate the component and lubrication in first chamber from the components and lubrication in the second chamber. By this arrangement, the respective components in the different chambers may be bathed in fluid lubricants specific to the needs and requirements of the components.
In a preferred method, the first chamber containing the friction plates may include a friction modifier, an additive that can be detrimental to lubricant seals associated with and fluid sealing the second chamber. Further, removable means are provided to access and fill the respective chambers.
Accordingly, an object of the invention is the provision of a limited slip differential for vehicle applications, where the differential casing includes at least a pair of fluid seals isolating the first chamber within the differential case from the second chamber between the differential case and the carrier.
Another object hereof is a method of operating a limited slip differential containing different sets of components, where the respective sets are bathed in different fluid lubricants.
Still another object hereof is a convenient, removable means to fill and maintain the respective fluid sealed chambers.
These and other objects of this invention will become more apparent in the description which follows, particularly when read in conjunction with the accompanying drawing.